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The efficient and selective light-driven conversion of carbon dioxide to formate is a scientific challenge for green chemistry and energy science, especially utilizing visible-light energy and earth-abundant catalytic materials. In this report, two mononuclear Ni(II) complexes of pyridylbenzimidazole (pbi) and pyridylbenzothiazole (pbt), such as Ni(pbt)(pyS)2 (1) and Ni(pbi)(pyS)2 (2) (pyS = pyridine-2-thiolate), were prepared and their reactivities studied. The two Ni complexes were examined for CO2 conversion using eosin Y as a photosensitizer upon visible-light irradiation in a H2O/ethanol solvent. The photoreaction of CO2 catalyzed by complexes 1 and 2 selectively affords formate with a high efficiency (14 000 turnover number) and a high catalytic selectivity of ∼99%. Undesirable proton reduction pathways were completely suppressed in the photocatalytic reactions with these sulfur-rich Ni catalysts under CO2. Hydrogen photoproduction was also studied under argon. Their kinetic isotope effects and influence of solution pH for formate and H2 production in the photocatalytic reactions are described in relation to the reaction mechanisms. These bioinspired Ni(II) catalysts with N/S ligation in relation to [NiFe]-hydrogenases are the first examples of early transition metal complexes affording such high selectivity and efficiencies, providing a future path to design solar-to-fuel processes for artificial photosynthesis.

Three ruthenium complexes containing a bidentate piq ligand, [(piq)Ru(bpy) 2 ] 2+ ( 1 ), [(piq)Ru(phen) 2 ] 2+ ( 2 ), and [(piq)Ru(DIP) 2 ] 2+ ( 3 ) (piq = phenylisoquinolinate, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, DIP = 4,7-diphenyl-1,10-phenanthroline), were prepared. The DNA binding properties of complexes 1 – 3 to double-stranded DNA were studied. The binding of 1 – 3 to calf-thymus DNA (ct-DNA) yielded lower emission intensities than those observed with the corresponding Ru complexes alone. To explore potential interactions of complexes 1 – 3 with lipid-rich organs in live cells, the emission properties of the Ru probes were studied with liposomes. The emission intensities of complexes 1 – 3 were enhanced to similar extents upon interaction with liposomes. The cytotoxic activities of the complexes against MDA-MB-231 and HUVECs were evaluated in vitro. The effects of complexes 1 – 3 on the survival of MDA-MB-231 cells were examined and compared with that of cis -platin. Complexes 2 and 3 were more cytotoxic to cancer cells than cis -platin. Complexes 1 – 3 showed cellular uptakes of 1.1, 10.6, and 76.6%, respectively, indicating that the greatest amount of complex 3 entered the cancer cells. Inhibition of cell migration by complexes 1 – 3 was also evaluated by the wound healing assay.

Two new dinuclear iridium (Ir) complexes bridged by a conjugated aromatic tppz ligand, (bhq)2Ir(tppz)Ir(bhq)2 (1) and (ppy)2Ir(tppz)Ir(ppy)2 (2) (bhq = benzo(h)quinolone, ppy = phenyl-pyridine, tppz = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine), were prepared. The DNA binding properties of complexes 1 and 2 were studied using single-stranded DNA, double-stranded DNA, and G-quadruplex DNA. G-Quadruplex binding was characterized by higher emission enhancements than those observed with other control DNA strands. Photophysical properties of complexes 1 and 2 indicated that 1 displayed selective G-quadruplex binding affinity, but 2 did not. The emission properties of complexes 1 and 2 were also studied using liposomes in order to understand their possible interactions with lipid-rich organelles in live cells. The phosphorescence intensity of 1 and 2 was enhanced upon interaction with liposomes, but 2 showed greater enhancement. We also confirmed that 1 and 2 could be used as probes in live cells. Complexes 1 and 2 were intensely stained in HeLa cervical cancer cells. Excitation with a λ = 488 nm laser showed red emission localized in the cytosol of cells. Cellular studies showed that 1 and 2 were located inside HeLa cells, but neither complex passed through the nuclear membrane. However, complexes 1 and 2 possessed superior photostability, indicating their role as good luminescent agents for imaging and tracking the endoplasmic reticulum (ER) in live cells. Overall, complex 1 exhibited better selectivity for G-quadruplexes, liposomes, and ER staining.

Single electron transfer (SET) promoted photoaddition reactions of N-α-trimethylsilylmethyl-N,N-dibenzylamines to fullerene C60 were investigated as part of an effort aimed at developing a general method to prepare various aryl ring containing aminomethylfullerenes and exploring factors that govern photoaddition efficiencies. The results show that the photoaddition reactions take place highly efficiently to form 1,2-adducts. The mechanism for this process involves generation of aminium radicals and C60 anion radical intermediates by a pathway initiated by excited state SET. SET is followed by desilylation of the aminium radicals to produce α-amino radicals that couple with either C60 or its radical anion to form precursors of the 1,2-adducts. The electronic nature of para-substituents on the aryl ring of N-α-trimethylsilylmethyl-N,N-dibenzylamines has a pronounced effect on the efficiency of the photoaddition reaction, with electron donating groups causing a greater than 2-fold enhancement compared to that brought about by electron withdrawing groups.

The selective assay of cyanide ions with a thioamide compound (HNPTU) containing phenol and pyridine as a chemosensor is reported using absorbance changes in a buffered aqueous solution (50 mM HEPES, pH 7.4) containing ethanol. Upon treatment with cyanide ions, the colorless solution of HNPTU turned yellow. No significant changes were observed with other comparable anions, such as F − , Cl − , Br − , I − , and CH 3 COO − . The color change of HNPTU upon treatment with CN − was maintained even in the presence of the comparable monovalent anions. The complex stability constant ( K a = 2.6 × 10 3 ) for the stoichiometric 1:1 complexation of HNPTU with cyanide ions was obtained based on absorbance titrations. The interaction of HNPTU with cyanide ions was proposed to be deprotonation, as shown by NMR and Cu(II) treatment experiments.

The catalytic effect of [M(2,2′-bipyridine) 2 (NO 3 )](NO 3 ) (M(bpy) 2 , M = Cu(II), Zn(II) and Cd(II)) on the super-coiled and double stranded DNA (scDNA and dsDNA) was examined by electrophoresis and a real-time detection linear dichroism (LD) technique. Although the Cu(bpy) 2 complex effectively cleaved both types of DNA, the other two complexes were inactive. This was explained by the electrochemical properties of the metal complexes. The Cu(bpy) 2 complex exhibited a redox potential at − 0.222 V with a peak to peak separation of 0.201 V, whereas the other two metal complexes did not undergo any redox reaction. Both electrophoresis and LD measurements revealed the superoxide radical, ·O 2 − , to be responsible for DNA cleavage. A kinetic study using the LD technique showed that the cleavage of dsDNA consisted of two first order reactions. The fast reaction is believed to reflect the cleavage of one strand, whereas the slow reaction involves the cleavage of the complementary strand at or near the first cleaved site.

A new zinc ion sensor 1-(anthracen-9-yl)- N -(pyridin-2-ylmethyl)- N -(quinolin-2-ylmethyl)methanamine 1 was synthesized by incorporating a dipicolylamine derivative as a binding unit and an anthracene group as a fluorescence signaling unit. The anthracene-based receptor 1 was highly selective for Zn 2+ with a fluorescence enhancement and a remarkable red shift in aqueous solution, whereas this chemosensor showed no response to other metals, especially Cd 2+ ion. The composition of the complex 1 –Zn 2+ turned out 1:1, based on Job’s plot, ESI-mass analysis, and 1 H NMR titration.

The catabolic acetolactate synthase (cALS) of Enterococcus faecalis V583 was cloned, expressed in Escherichia coli, and purified to homogeneity. The purified protein had a molecular weight of 60 kDa. The cALS of E. faecalis is highly homologous with other cALSs, while sharing low homology with its anabolic counterparts. The cALS of E. faecalis exhibits optimum activity at a temperature of 37 °C and pH 6.8. Based on the enzyme characterization, the apparent Km for pyruvate was calculated to be 1.37 mM, while the Kc for thiamin diphosphate (ThDP) and Mg2+ were found to be 0.031 μM and 1.27 mM, respectively. Negligible absorbance at 450 nm and lack of activity enhancement upon addition of flavin adenine dinucleotide (FAD) to the assay buffer suggest that the cALS of E. faecalis is not FAD-dependent. The enzyme showed extreme stability against the organic solvent dimethyl sulfoxide (DMSO), whereas the activity decreased to less than 50% in the presence of acetone and ethanol.

The photocatalyst-enzyme coupled system for artificial photosynthesis process is one of the most promising methods of solar energy conversion for the synthesis of organic chemicals or fuel. Here we report the synthesis of a novel graphene-based visible light active photocatalyst which covalently bonded the chromophore, such as multianthraquinone substituted porphyrin with the chemically converted graphene as a photocatalyst of the artificial photosynthesis system for an efficient photosynthetic production of formic acid from CO(2). The results not only show a benchmark example of the graphene-based material used as a photocatalyst in general artificial photosynthesis but also the benchmark example of the selective production system of solar chemicals/solar fuel directly from CO(2).

In this study, an assay to quantify the presence of aluminum ions with a receptor containing naphthol and quinoline moieties was developed using a turn-on fluorescence enhancement approach. Upon treatment with aluminum ions, the fluorescence of the receptor was enhanced at 510 nm due to the formation of a complex between the ligand and aluminum ions at room temperature. As the concentration of Al3+ was increased, the fluorescence gradually increased. Other metal ions, such as K+, Ag+, Ca2+, Mg2+, Zn2+, Mn2+, Co2+, Ni2+, Cu2+, Cd2+, Cr3+, Fe3+, In3+, had no significant effect on the fluorescence.

The protective antigen (PA) of Bacillus anthracis is a secreted protein that functions as a critical virulence factor. Protective antigen has been selected as a biomarker in detecting bacterial infection. The in vitro selection method, systematic evolution of ligands by exponential enrichment (SELEX), was used to find single-stranded DNAs that were tightly bound to PA. After 8 rounds of the SELEX process with PA, 4 different oligonucleotides (referred to as aptamers) that contain a 30-residue ssDNA sequence were identified. Dissociation constant (K(d)) values with Cy3-attached aptamers were determined via fluorophotometry to be within a nanomolar range. The authors attempted to visualize the detection of PA using an aptamer-based enzyme-linked immunosorbent assay method, which has proven to be successful within a nanomolar K(d) value range. Furthermore, 2 of the 4 aptamers exhibited specificity to PA against bovine serum albumin and bovine serum. The results of this study demonstrate the analytical potential of an oligonucleotide-based biosensor for a wide variety of applications, particularly in diagnosing disease through specific protein biomarkers.

Fructose-1,6-bisphosphate (FBP) aldolase, is a glycolytic enzyme that catalyzes the reversible condensation reaction of FBP to dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P). The aldolase gene from Aquifex aeolicus was subcloned, overexpressed in E. coli and purified to 95% homogeneity. The purified enzyme was activated by high concentrations of NH 4 + and low concentrations of Co 2+ . The native molecular weight of the purified FBP aldolase was identified as 67 kDa (dimer) by gel filtration chromatography. The enzyme exhibits optimum pH at 6.5 and temperature at 90 °C. Based on the kinetic characterizations, the apparent K m was calculated to be 4.4 ± 0.07 mM, while V max was found to be 100 ± 0.02 μM min −1 mg protein −1 . The recombinant protein showed extreme heat stability; no activity loss was observed even at 100 °C for 2 h. In addition, the thermophilic enzyme also showed higher stability against several organic solvents viz . acetonitrile, 1,4-dioxane, and methanol. With higher stability against both heat and organic solvents than any other class II aldolase, the A. aeolicus FBP aldolase is an attractive enzyme for use as a biocatalyst for industrial applications.

Acetohydroxyacid synthase (AHAS, EC 2. 2. 1. 6) is the enzyme that catalyses the first step in the common pathway of the biosynthesis of the branched chain amino acids, valine, leucine and isoleucine. For the first time, the AHAS gene from Bacillus anthracis was cloned into the expression vector pET28a(+), and was expressed in the E. coli strain BL21(DE3). The purified enzyme was checked on 12% SDS-PAGE to be a single band with molecular weight of 65 kDa. The optimum pH and temperature for B. anthracis AHAS was at pH 7.5 and 37 °C, respectively. Kinetic parameters of B. anthracis were as follows: K m for pyruvate, K 0.5 for ThDP and Mg 2+ was 4.8, 0.28 and 1.16 mM respectively. AHAS from B. anthracis showed strong resistance to three classes of herbicides, Londax (a sulfonylurea), Cadre (an imidazolinone), and TP (a triazolopyrimidine). These results indicated that these herbicides could be used in the search for new anti-bacterial drugs.

A series of structurally-related [Cu(R-benzyl-dipicolylamine)(NO3)2] complexes, where R=methoxy- (1), methyl- (2), H- (3), fluoro- (4), and nitro-group (5), were synthesized, and their activity on DNA cleavage was investigated by linear dichroism (LD) and electrophoresis. The addition of a benzyl group to the dipicolylamine ligand of the [Cu(dipicolylamine)(NO3)2] complex (A), i.e., the [Cu(benzyl-dipicolylamine)(NO3)2] complex (3), caused significant enhancement in the efficiency of oxidative cleavage of both super-coiled (sc) and double stranded (ds) DNA, as evidenced by the electrophoresis pattern and faster decrease in the LD intensity at 260nm. The efficiency in DNA cleavage was also altered with further modifications of the benzyl group by the introduction of various substituents at the para-position. The cleavage efficiency appeared to be the largest when the methyl group was attached. The order of efficiency in DNA cleavage was methyl>methoxy≈H>fluoro≈nitro group. When an electron-withdrawing group was introduced, the cleavage efficiency decreased remarkably. The reactive oxygen species involved in the cleavage process were the superoxide radical and singlet oxygen. A possible mechanism for this variation in the DNA cleavage efficiency was proposed.

There is an intriguing, current controversy on the involvement of iron(III)-hydroperoxo species as a "second electrophilic oxidant" in oxygenation reactions by heme and non-heme iron enzymes and their model compounds. In the present work, we have performed reactivity studies of the iron-hydroperoxo species in nucleophilic and electrophilic reactions, with in situ-generated mononuclear non-heme iron(III)-hydroperoxo complexes that have been well characterized with various spectroscopic techniques. The intermediates did not show any reactivities in the nucleophilic (e.g., aldehyde deformylation) and electrophilic (e.g., oxidation of sulfide and olefin) reactions. These results demonstrate that non-heme iron(III)-hydroperoxo species are sluggish oxidants and that the oxidizing power of the intermediates cannot compete with that of high-valent iron(IV)-oxo complexes. We have also reported reactivities of mononuclear non-heme iron(III)-peroxo and iron(IV)-oxo complexes in the aldehyde deformylation and the oxidation of sulfides, respectively.

The air-stable complex [Fe(6-Me3-TPA) (O2CAr)]+ [1; 6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine] has been synthesized as a model for the iron(II) site of lipoxygenase. This iron(II) complex reacts with 0.5 equiv ROOH to form a yellow species, which has been formulated as [FeIII(OH)(6-Me3-TPA) (O2CAr)]+ (2) by electrospray mass spectrometry. Addition of more ROOH converts 2 into a purple species, which is characterized by electrospray ionization mass spectrometry and resonance Raman spectroscopy as [FeIII(OOR)(6-Me3-TPA)(O2CAr)]+. The purple species is metastable and decomposes via Fe-O bond homolysis to regenerate the starting iron(II) complex. These metal-centered transformations parallel the changes observed for lipoxygenase in its reaction with its product hydroperoxide.

Our efforts to model the oxygen activation chemistry of nonheme iron enzymes have yielded transient intermediates with novel properties. These properties can be dramatically affected by the introduction of a 6-methyl substituent on the pendant pyridines of the tetradentate ligand TPA (TPA = tris(2-pyridylmethyl)amine). A series of Fe(TPA) complexes has thus been synthesized and characterized to provide the structural basis for these dramatic effects. The following complexes have been obtained: [Fe(L)(CH3CN)2](ClO4)2 (1, L = TPA; 2, L = 6-MeTPA; 3, L = 6-Me2TPA; 4, L = 6-Me3TPA) and [Fe(L)(acac)](ClO4)2 (5, L = TPA; 6, L = 5-Me3TPA; 7, L = 6-MeTPA). As indicated by 1H NMR and/or EPR, 1, 5, and 6 with no 6-methyl substituent are low spin, while complexes 2, 3, 4, and 7 with at least one 6-methyl substituent are all high spin, with higher redox potentials than their low-spin counterparts. The ligands with 6-methyl substituents thus favor a metal center with a larger ionic radius, i.e., FeII over FeIII and h...

The efficiency of [Cu(2,2′-bipyridine) 2 (NO 3 )]NO 3 , [Cu(2,2′-dipyridylamine) 2 (NO 3 ) 2 ], and [Cu(dipicolylamine) 2 (NO 3 ) 2 ] complexes (complex 1, 2 and 3, respectively) in oxidative DNA cleavage was examined by electrophoresis and linear dichroism (LD). Among the three Cu complexes, complex 1 showed the highest efficiency in super-coiled DNA (scDNA) cleavage in electrophoresis. The presence of tiron, a superoxide radical scavenger, suppressed the reaction almost completely. The LD signal at 260 nm decreased gradually as the time passed. The decrease in LD magnitude was explained best by the sum of the two single exponential curves. This suggests that the cleavage reaction involves two first order kinetic processes; an increase in flexibility due to scission of one of the strands and a shortening in the DNA stem due to cut of both strands of double stranded DNA (dsDNA). In agreement with the electrophoresis data, complex 1 exhibited the highest efficiency with the superoxide radical found to be the essential reactive oxygen species. The order of efficiency in both scDNA and dsDNA was as follows: complex 1 > complex 2 > complex 3. The electrochemical properties alone were insufficient to explain the observed efficiencies, even though reduction of the central Cu ion is essential for the oxidative DNA cleavage. This highlights the importance of an ability to ligate the molecular oxygen (or hydrogen peroxide) to the central Cu ion to produce the superoxide radical, in addition to the reduction of Cu ion, in oxidative DNA cleavage.

The reactivity of ([mu]-oxo)diferric complexes with [sup t]BuOOH (TBHP) for the functionalization of alkanes in CH[sub 3]CN has been investigated as part of our efforts to model dinuclear sites in nonheme iron enzymes. [Fe[sub 2](TPA)[sub 2]O(OAc)](CIO[sub 4])[sub 3] (1) (TPA = tris(2-pyridylmethyl)amine, OAc = acetate) is an efficient catalyst for cyclohexane oxidation, affording cyclohexanol (A, 9 equiv), cyclohexanone (K, 11 equiv), and (tert-butylperoxy)cyclohexane (P, 16 equiv) in 0.25 h at ambient temperature and pressure under an argon atmosphere. The catalyst is remarkably robust, as indicated by the [sup 1]H NMR and UV-vis spectra of the reaction mixture during the catalytic reaction and by its ability to maintain its turnover efficiency with subsequent additions of oxidant. The catalytic mechanism for TBHP utilization was explored by observing the effects of varying the tripodal ligands on the ([mu]-oxo)([mu]-carboxylato)diferric catalysts and varying the bridge on Fe[sub 2]O(TPA)[sub 2] catalysts. The (A + K)/P ratio increased as the ligands became more electron donating. Solvent also played an important role in determining the partitioning of products between A + K and P, with benzonitrile favoring hydroxylated products at the expense of P and pyridine having the opposite effect. 49 refs., 2 figs., 3 tabs.

Terminal 1,2- or 1,3-diol acetonides can be converted regioselectively into secondary 1-methylcyclopropyl (MCP) ether or primary triethylsilyl ethers under mild conditions. MCP ethers are stable to a variety of conditions and can be removed by treatment with NBS or DDQ.

Alpha and beta tubulin genes were cloned from the Capsicum annuum leaves using rapid amplification of cDNA ends (RACE)-PCR. Nucleotide sequence analysis revealed that 1,353 bp Capsicum annuum alpha/beta-tubulin (CAnm alpha/beta-TUB) encodes a protein of 450 amino acids (aa) each. The recombinant alpha/beta tubulin was overexpressed mainly as an inclusion body in Escherichia coli BL21 (DE3), upon induction with 0.2 mM isopropyl-beta-D-thiogalactopyranoside (IPTG), and its content was as high as 50% of the total protein content. Effective fusion protein purification and refolding are described. The average yields of alpha and beta tubulin were 2.0 and 1.3 mg/l of culture respectively. The apparent molecular weight of each tubulin was estimated to be 55 kDa by SDS-polyacrylamide gel electrophoresis (PAGE). The tubulin monomers were found to be assembly competent using a standard dimerization assay, and also retained antigenicity with anti-His/T7 antibodies. The purified tubulins were polymerized to microtubule-like structures in the presence of 2 mM guanosine 5'-triphosphate (GTP).

Mononuclear nonheme oxoiron(IV) complexes bearing 15-membered macrocyclic ligands were generated from the reactions of their corresponding iron(II) complexes and iodosylbenzene (PhIO) in CH 3 CN. The oxoiron(IV) species were characterized with various spectroscopic techniques such as UV–vis spectrophotometer, electron paramagnetic resonance, electrospray ionization mass spectrometer, and resonance Raman spectroscopy. The oxoiron(IV) complexes were inactive in olefin epoxidation. In contrast, when iron(II) or oxoiron(IV) complexes were combined with PhIO in the presence of olefins, high yields of epoxide products were obtained. These results indicate that in addition to the oxoiron(IV) species, there must be at least one more active oxidant (e.g., Fe IV -OIPh adduct or oxoiron(V) species) that effects the olefin epoxidation. We have also demonstrated that the ligand environment of iron catalysts is an important factor in controlling the catalytic activity as well as the product selectivity in the epoxidation of olefins by PhIO.

The oxygenation of carbon-carbon double bonds by iron enzymes generally results in the formation of epoxides, except in the case of the Rieske dioxygenases, where cis-diols are produced. Herein we report a systematic study of olefin oxidations with H(2)O(2) catalyzed by a group of non-heme iron complexes, i.e., [Fe(II)(BPMEN)(CH(3)CN)(2)](2+) (1, BPMEN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) and [Fe(II)(TPA)(CH(3)CN)(2)](2+) (4, TPA = tris(2-pyridylmethyl)amine) and their 6- and 5-methyl-substituted derivatives. We demonstrate that olefin epoxidation and cis-dihydroxylation are different facets of the reactivity of a common Fe(III)-OOH intermediate, whose spin state can be modulated by the electronic and steric properties of the ligand environment. Highly stereoselective epoxidation is favored by catalysts with no more than one 6-methyl substituent, which give rise to low-spin Fe(III)-OOH species (category A). On the other hand, cis-dihydroxylation is favored by catalysts with more than one 6-methyl substituent, which afford high-spin Fe(III)-OOH species (category B). For catalysts in category A, both the epoxide and the cis-diol product incorporate (18)O from H(2)(18)O, results that implicate a cis-H(18)O-Fe(V)=O species derived from O-O bond heterolysis of a cis-H(2)(18)O-Fe(III)-OOH intermediate. In contrast, catalysts in category B incorporate both oxygen atoms from H(2)(18)O(2) into the dominant cis-diol product, via a putative Fe(III)-eta(2)-OOH species. Thus, a key feature of the catalysts in this family is the availability of two cis labile sites, required for peroxide activation. The olefin epoxidation and cis-dihydroxylation studies described here not only corroborate the mechanistic scheme derived from our earlier studies on alkane hydroxylation by this same family of catalysts (Chen, K.; Que, L, Jr. J. Am. Chem. Soc. 2001, 123, 6327) but also further enhance its credibility. Taken together, these reactions demonstrate the catalytic versatility of these complexes and provide a rationale for Nature's choice of ligand environments in biocatalysts that carry out olefin oxidations.

Axial ligand substitution of a mononuclear nonheme oxoiron(IV) complex, [FeIV(O)(TMC)(NCCH3)]2+ (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), leads to the formation of new FeIV=O species with relatively intense electronic absorption features in the near-UV region. The presence of these near-UV features allowed us to make the first observation of Fe=O vibrations of S = 1 mononuclear nonheme oxoiron(IV) complexes by resonance Raman spectroscopy. We have also demonstrated that the reactivity of nonheme oxoiron(IV) intermediates is markedly influenced by the axial ligands.

We have used dioxygen, not artificial oxidants such as peracids, iodosylarenes, and hydroperoxides, in the generation of a mononuclear nonheme oxoiron(IV) complex, [Fe(IV)(TMC)(O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), from its corresponding Fe(II) complex, [Fe(TMC)(CF3SO3)2]. The formation of oxoiron(IV) species by activating dioxygen was markedly dependent on iron(II) complexes and solvents, and this observation was interpreted with the electronic effect of iron(II) complexes on dioxygen activation to form oxoiron(IV) species. A catalytic aerobic oxidation of organic substrates was demonstrated in the presence of the [Fe(TMC)]2+ complex. By carrying out 18O-labeled water experiment, we were able to conclude that the oxidation of organic substrates was mediated by an oxoiron(IV) intermediate, not by a radical type of autoxidation process.

Nonheme oxoiron(IV) complexes of two pentadentate ligands, N4Py (N,N-bis(2-pyridylmethyl)-bis(2-pyridyl)methylamine) and Bn-tpen (N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-diaminoethane), have been generated and found to have spectroscopic properties similar to the closely related tetradentate TPA (tris(2-pyridylmethyl)amine) complex reported earlier. However, unlike the TPA complex, the pentadentate complexes have a considerable lifetime at room temperature. This greater thermal stability has allowed the hydroxylation of alkanes with C-H bonds as strong as 99.3 kcal/mol to be observed at room temperature. Furthermore, a large deuterium KIE value is found in the oxidation of ethylbenzene. These observations lend strong credence to postulated mechanisms of mononuclear nonheme iron enzymes that invoke the intermediacy of oxoiron(IV) species.

We report in this study that an oxoiron(IV) porphyrin complex bearing electron-deficient porphyrin ligand, (TPFPP)FeIV=O (TPFPP = meso-tetrakis(pentafluorophenyl)porphinato dianion), shows reactivities similar to those found in oxoiron(IV) porphyrin pi-cation radicals. In the epoxidation of olefins by the (TPFPP)FeIV=O complex, epoxides were yielded as major products; cyclohexene oxide was the sole product formed in the epoxidation of cyclohexene, and stilbenes were stereospecifically oxidized to the corresponding epoxide products. More striking results were obtained in alkane hydroxylation reactions; the hydroxylation of adamantane afforded a high degree of selectivity for tertiary C-H bonds over secondary C-H bonds, and the hydroxylation of cis-1,2-dimethylcyclohexane yielded a tertiary alcohol product with >99% retention of stereochemistry. The latter result demonstrates that an oxoiron(IV) porphyrin complex hydroxylates alkanes with a high stereospecificity. Isotope labeling studies performed with H218O and 18O2 in the olefin epoxidation and alkane hydroxylation reactions demonstrated that oxygen atoms in oxygenated products derived from the oxoiron(IV) porphyrin complex.

A homogeneous assay of the protective antigen in anthrax toxin is reported using two new PA-specific aptamers for selective and sensitive detection, based on reduction in the fluorescence emission according to the formation of the aptamer-PA ternary complex. PA at 1 nM was readily detected using OliGreen as a fluorophore in HEPES buffer. We also demonstrated that the PA detection could be performed in blood serum. The binding interaction between the aptamer and PA was strong enough to dehybridize double-stranded DNA paired completely with 12 bases at room temperature. Moreover, this fluorescence study revealed that the binding sites of the two aptamers were located differently on the PA protein. We believe our approach may lay the groundwork for the real-time detection of PA.